Effects of the Control Parameters on the Stability of a Laminar Boundary Layer on a Porous Flat Plate

This work is devoted to the analysis of the linear temporal stability of a laminar dynamic boundary layer on a horizontal porous plane plate. The basic flow is assumed to be laminar and two-dimensional. The basic flow velocity profiles are obtained by numerically solving the Blasius equation using the Runge-Kutta method. The perturbations of these basic solutions are expressed in the form of three-dimensional Tollmien-Schlichting waves. The formulation of the stability problem leads to the Orr-Sommerfeld equation modified by the permeability parameter (Darcy number) and the small Reynolds number. This equation is given in a general form which can be applied to the Chebyshev domain and the boundary layer domain and solved numerically using the Chebyshev spectral collocation method. The marginal stability diagrams, the critical Reynolds numbers and the eigenvalue spectra are obtained for different values of the parameters which have modified the stability equation. Numerical solutions indicate the importance of the effect of these parameters on the flow stability characteristics.

Numerical Simulation of Laminar Boundary Layer Flow Over a Horizontal Flat Plate in External Incompressible Viscous Fluid

In this paper, steady laminar boundary layer flow of a Newtonian fluid over a flat plate in a uniform free stream was investigated numerically when the surface plate is heated by forced convection from the hot fluid. This flow is a good model of many situations involving flow over fins that are relatively widely spaced. All the solutions given here were with constant fluid properties and negligible viscous dissipation for two-dimensional, steady, incompressible laminar flow with zero pressure gradient. The similarity solution has shown its efficiency here to transform the governing equations of the thermal boundary layer into a nonlinear, third-order ordinary differential equation and solved numerically by using 4th-order Runge-Kutta method which in turn was programmed in FORTRAN language. The dimensionless temperature, velocity, and all boundary layer functions profiles were obtained and plotted in figures for different parameters entering into the problem. Several results of best approximations and expressions of important correlations relating to heat transfer rates were drawn in this study of which Prandtl’s number to the plate for physical interest was also discussed across the tables. The same case of solution procedure was made for a plane plate subjected to other thermal boundary conditions in a laminar flow. Finally, for the validation of the treated numerical model, the results obtained are in good agreement with those of the specialized literature, and comparison with available results in certain cases is excellent.

Functionally Graded Plate Fracture by Field Boundary Element

The paper describes the Field Boundary Element Method applied to the fracture analysis of a 2D rectangular plate made of Functionally Graded Material to calculate Mode I Stress Intensity Factor. The object of the Field Boundary Element Method is the transversely isotropic plane plate. Its material presents an exponential variation of the elasticity tensor depending on a scalar function of position, i.e., the elastic tensor results from multiplying a scalar function by a constant taken as a reference. Several examples using a parametric representation of the structural response show the suitability of the method that constitutes a sight of Stress Intensity Factor evaluation of Functionally Graded Materials plane plates even in the case of more complex geometries.

Thermo elasto-plastic contact analysis for high temperature applications

This study presents the development of a thermo-mechanical simulation model for an elastic-plastic contact problem between a half cylinder and a plane plate. The set of equations was solved using direct coupling method by Ansys mechanical. The results obtained from the present numerical model of the structural contact without heat transfer are compared with those of analytical, experimental and other numerical models. Then, the contact problem was solved using a coupled thermo-mechanical model. Computational results showed significant effects of thermal consideration in the elastic-plastic contact problem. Large deformations of structure due to high temperature are predicted using the thermo-mechanical model with elastic-plastic deformations. This model is useful to predict deformations on the structural components due to contact at high temperature situation.

Unsteady Collisionless Gaseous Plasma Flow in the Upper Layers of the Charged Atmosphere and The Investigation of Vlasov-Maxwell Equations System.

In the upper charged layers of the atmosphere, the plasma is very rarefied. The collisions between its molecules are almost non-existent, and the driving forces behind them are the Lorentz forces resulting from the electric and magnetic fields. For this reason, we are interested in studying the behavior of non-collision plasmas because of its essential applications, such as the movement of satellites in the charged atmosphere. In this paper, the flow problem of collisionless gaseous plasma is examined. For that propose, we solve the unsteady Vlasov-Maxwell system of non-linear partial differential equations analytically. Methods of moments and traveling wave parameters are used to acquire an exact solution. Specific macroscopic properties of collisionless gaseous plasma are calculated along with electrical and magnetic fields. Further, thermodynamic estimation, such as entropy and entropy production, is presented. Those calculations allow us to measure the consistency with the laws of non-equilibrium thermodynamics. Relations between internal energy modification participations are predicted using Gibbs' equation for collisionless plasma. The modification effect of internal energies due to electro-magnetic fields is found to be small compared with the internal energy change due to the effect of entropy. That is because these fields are self-induced by plasma particles due to the sudden movement of the rigid plane plate. The results are accomplished according to the typical argon gaseous plasma model. Three-dimensional diagrams showing the measured variables are drawn to investigate and discuss their behavior. The problem has many commercial applications for the movement of objects in the charged atmosphere.

Design and analysis microstrip antenna with reflector to enhancement gain for wireless communication

In this paper is presented the good solution to enhancement gain by using physical plane plate reflector with optimum distance by a reflector was used with the antenna and using a sweep parameter for the distance at which the reflector was placed at (, we found the best distance is when selected the bandwidth is 28GHz where . The gain at the bandwidth in 28GHz was improved from (5.48, 6.78, and 7.83) dB to 11.53 dB, while the gain without a reflector is 7.1 dB. The simulation results were obtained using CST which was more consistent with the practical results.

Selective Lamb Mode Transmission Enabled by Local Resonance Based Ultrasonic Metamaterial

In this study, a kind of elastic metamaterial substructure was designed for the selective mode filtering and transmission of symmetric and antisymmetric elastic waves. It is composed of double-sided aluminum-lead composite cylinders arranged in a periodic pattern bounded on an aluminum plate. The band structure of elastic metamaterial unit cell is numerically investigated using the modal analysis of a finite element model (FEM) by treating a unit microstructural cell with the Bloch-Floquet boundary condition. Through analyzing the vibration modes of the unit cell, a complete antisymmetric wave bandgap and a complete symmetric wave bandgap can be formed in different frequency ranges. Considering the geometric complexity of the designed substructure, the dynamic effective mass density of the proposed metamaterial unit cell is calculated by considering the structure as a homogeneous medium under the sub-wavelength requirement. The negative effective mass density behavior for in-plane and out-of-plane plate modes will be presented to verify the bandgap effect of different wave modes. A FEM harmonic analysis is further conducted to obtain the spectral response of a chain model and explore the mode filtering efficiency. Finally, a coupled field transient dynamic FEM is carried out to acquire the dynamic response of the structure. The frequency-wavenumber analysis demonstrates the successful achievement of model filtering behavior. The proposed selective mode transmission control methodology possesses great potential in future SHM and NDE applications. A case study for S0 mode conversion to SH0 mode using a different metamaterial unit cell is exhibited to illustrate other wave control capabilities. The paper finishes with summary, concluding remarks, and suggestions for future work.

High precise and zero-cost solution for fully automatic industrial robot TCP calibration

Purpose The purpose of this study is to present a novel method for industrial robot TCP (tool center point) calibration. The proposed method offers fully automated robot TCP calibration within a defined cycle time. The method is applicable for large-scale installations due to its zero cost for each robot. Design/methodology/approach Precise and expensive measuring equipment or specially designed reference devices are required for robot calibration. The calibration can be performed by using only one plane plate in this method, and the calibration procedure is defined step by step: the robot moves to the target plane position. Then, the TCP touches the plane and the actual robot configuration is recorded. Then robot moves back into position and the same step is repeated for a new sample. Alternatively, the robot can be stationary and the plane can be moved towards the robot TCP. TCP is calculated by processing the difference of the contact points recorded at different positions. The process is fully automated. No special equipment is used. The calculations are very simple, and the robot controller can easily be realized. Findings The conventional manual robot TCP calibration process takes about 15 min and takes more time in case of the high accuracy. The proposed method reduces this time to less than 3 min without operator support. Practical tests have shown that TCP calibration can be performed with 0.1-0.6 mm of accuracy. This solution is an automated process and does not require special installation and it also has approximately zero cost. For this reason, this study recommends using the proposed solution widely in areas where even one or hundreds of robots are located. Research limitations/implications In this study, the data were directly taken from the robot controller without using any special measuring equipment. The industrial robot used in the tests has no absolute calibration. The classical “four-point method” was used for reference TCP data. It is the initial acceptance that this process conducted with extreme care and by using a needle-tipped tool will not produce exact values. It was observed that deviation of the TCP from a fixed point in reorient motions was not more than 0.5 mm. This method has been validated for different bits. The pilot works for different robot applications in Ford Otosan Gölcük Plant have been completed and dissemination has started. Originality/value Although the approach uses is clear and simple, it is surprising that the calculation of TCP using plane equations has so far not been mentioned in the literature. The disadvantage of using either fixed point or sphere as a reference is that the TCP cannot automatically guide to the target. This problem was overcome with the use of a larger target plane plate and the process was fully automated. The proposed method can be widely used in practical applications.

Development of a model for thin films and numerical sensitivity tests

Because the unsteady behavior of liquid films in steam turbines is a key point for additional friction losses and atomization process (that leads to coarse water generation), the development of a dedicated model has been found necessary. A two-dimensional computational fluid dynamics code for unstructured mesh is being developed using the finite volume method to simulate this thin liquid film. The aim is to predict the formation of the waves in the film since it is suspected to be a key parameter for friction and atomization. Applied as a first step to a plane plate, the code has been verified in a one-dimensional version with analytical solutions and is tested in low-pressure turbine steam conditions. Falling films computations (without gas shear stress) show that the model is capable to reproduce the waves’ shape of experiments from the literature. With steam under low-pressure turbine conditions, and compared to experimental data from the University of Michigan, the model including shear stress and surface tension provides good results for heights. Sensitivity calculations have been undergone showing the crucial influence of the surface tension and the generation of solitary waves for high velocities is captured by the code. The effect of gravity is also quantified.